The present invention relates to a technology for processing an evaporative fuel generated in a fuel tank or the like provided in parallel to an internal combustion engine of an automobile or the like.
Concerning the internal combustion engine mounted in an automobile or the like, the development of a lean-burn internal combustion engine capable of burning a mixture having air/fuel ratio (excessive oxygen state) higher than a theoretical air/fuel ratio has been pursued for reducing a consumption amount of fuel. As such a lean-burn internal combustion engine, there is known an internal combustion engine of an in-cylinder injection type in which a fuel injection valve is mounted such that an injection hole faces a combustion chamber.
In the in-cylinder injection type internal combustion engine, in a low-load operating region, new air is introduced into the combustion chamber in an intake stroke, fuel is injected from the fuel injection valve in a subsequent compression stroke so that a combustible mixture is formed only in the vicinity of an ignition plug. That is, the mixture in the combustion chamber becomes a so-called stratified state which has a combustible mixture layer in the vicinity of the ignition plug, and an air layer in other region except in the vicinity of the ignition plug. In the case of the stratified mixture, the combustible mixture layer in the vicinity of the ignition plug is burned as an ignition source.
In the case of the in-cylinder injection type internal combustion engine, new air is introduced into the combustion chamber in the intake stroke in a medium-load operating region, and fuel is injected from the fuel injection valve at the same time. At that time, an amount of fuel injected from the fuel injection valve is an amount in which a ratio of an amount of new air to an amount of fuel is higher than the theoretical air/fuel ratio. In this case, lean mixture in which fuel and new air are uniformly mixed is formed substantially in the entire region in the combustion chamber.
In the case of the in-cylinder injection type internal combustion engine, new air is introduced into the combustion chamber in the intake stroke in a high-load operating region, and fuel is injected from the fuel injection valve at the same time. At that time, an amount of fuel injected from the fuel injection valve is an amount in which a ratio of an amount of new air to an amount of fuel is substantially equal to the theoretical air/fuel ratio. In this case, stoichiometric mixture in which fuel and new air are uniformly mixed is formed in the entire region in the combustion chamber.
In the case of the in-cylinder injection type internal combustion engine, since the lean-burn can be realized in the low-load and medium-load operating regions in this manner, a fuel consumption amount can largely be reduced.
On the other hand, an evaporative fuel processing apparatus is provided in an internal combustion engine for processing evaporative fuel generated in a fuel tank or the like. Such an evaporative fuel processing apparatus is composed of a charcoal canister for once storing evaporative fuel generated in the fuel tank, an atmosphere introducing passage for introducing atmosphere into the charcoal canister, a negative pressure introducing passage for introducing an intake pipe negative pressure generated in an intake passage downstream of a throttle valve into the charcoal canister, and a flow rate control valve for adjusting flow rate in the negative pressure introducing passage.
In the evaporative fuel processing apparatus structured as described above, the evaporative fuel generated in the fuel tank is adsorbed by an adsorbent such as active carbon incorporated in the charcoal canister while a flow rate control valve is closed. If the flow rate control valve is opened, an intake pipe negative pressure generated in the intake passage is applied to the charcoal canister through the negative pressure introducing passage, and the charcoal canister is evaporated into negative pressure. If the pressure in the charcoal canister becomes negative, the atmosphere is drawn from the atmosphere introducing passage into the charcoal canister, and the atmosphere drawn into the charcoal canister is drawn into the intake passage through the negative pressure introducing passage. That is, a flow of atmosphere flowing through the charcoal canister is generated.
The evaporative fuel adsorbed by the adsorbent in the charcoal canister is separated from the adsorbent due to the atmosphere flowing through the charcoal canister, and is introduced into the intake passage together with the atmosphere. The evaporative fuel introduced into the intake passage is introduced into the combustion chamber of the internal combustion engine while being mixed with new air from upstream the intake passage, and is burned and processed together with fuel injected from the fuel injection valve.
In the in-cylinder injection type internal combustion engine, the throttle valve is substantially fully opened in most of the operating regions except at the time of extremely low-load operating so as to reduce the driving loss due to a pumping function and therefore, the intake pipe negative pressure is not generated easily in the intake passage downstream the throttle valve. As a result, it is difficult to form a flow of atmosphere flowing through the charcoal canister, and it is difficult to introduce the evaporative fuel in the charcoal canister into the intake system and to process the same.
With respect to such a problem, there is known an evaporative fuel processing apparatus for an internal combustion engine described in Japanese Patent Application Laid-open No.5-71430. According to this evaporative fuel processing apparatus for an internal combustion engine, an atmosphere intake of the charcoal canister and an intake pipe negative pressure intake are opened in an engine intake passage which generates substantially the same static pressure, and an opening direction of the air intake is directed toward the upstream portion of the intake air flow, thereby introducing the evaporative fuel into the engine intake passage utilizing a difference in pressure between the dynamic pressure of the intake air flow acting on the air intake and the static pressure acting on the intake negative pressure intake.
However, in the case that the throttle valve is substantially fully opened, a difference between the static pressure and the dynamic pressure of the intake air flow is substantially constant over a wide operating region. Therefore, in the case that the amount of evaporative fuel is abruptly increased such when a temperature in the fuel tank rises, there is a problem that the evaporative fuel can not be introduced into the intake system so that all the evaporative fuel can not be processed.
Further, in the case that the evaporative fuel processing apparatus is applied to the in-cylinder injection type internal combustion engine, if the in-cylinder injection type internal combustion engine is in the stratified combustion operating state, since the evaporative fuel is supplied into the combustion chamber while being mixed with intake air, there is a problem that a stratified state is not established in the combustion chamber, and the combustion state becomes unstable.
With respect to such a problem, there is known an in-cylinder injection type internal combustion engine described in Japanese Patent Application Laid-open No. 4-194354. In this in-cylinder injection type internal combustion engine, evaporative fuel is supplied to an intake passage only when an engine load is equal to or greater than a predetermined authorized load. That is, the evaporative fuel is supplied to the intake passage only when the internal combustion engine is in a homogenous combustion operating state so that the evaporative fuel is processed without unstabilizing the combustion state.
However, in the in-cylinder injection type internal combustion engine, since the throttle valve is substantially fully opened even at the time of the homogenous combustion operating, it is difficult to generate the intake pipe negative pressure in the intake passage downstream the throttle valve. Therefore, in the case that the amount of evaporative fuel is abruptly increased, there is a problem that all the evaporative fuel can not be processed.
On the other hand, in the in-cylinder injection type internal combustion engine, a method for controlling the throttle valve toward the closing side so as to increase the intake pipe negative pressure might seem to be possible. However, since degree of negative pressure of the intake pipe negative pressure is abruptly increased, the amount of evaporative fuel to be supplied to the internal combustion engine is abruptly increased, and there is a problem that the combustion state of the internal combustion engine becomes unstable.